One mole of hydrogen gas burns in excess of oxygen to give 290 kJ of heat. What is the amount of heat produced when 4g of hydrogen gas is burnt under the same conditions ?

One mole of H2 releases 290 kJ on combustion; to find heat for 4 g H2 convert mass to moles. A hydrogen molecule H2 consists of two hydrogen atoms (atomic number 1), so the molar mass of H2 is 2 g mol–1; therefore 4 g corresponds to 4 ÷ 2 = 2 mol of H2 [1]. Enthalpy of combustion values are given per mole of substance burned; thus heat released scales with the number of moles consumed. Burning 2 mol of H2 at the same conditions gives 2 × 290 kJ = 580 kJ of heat. Hence option 3 (580 kJ) is correct.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59